1. Field of the Invention
The present invention relates to a rubber composition for a tire. More specifically it relates to a rubber composition suitable for use as a tread for a tire, especially a tire for icy and snowy road, having an improved ice traction, while maintaining abrasion resistance, by blending an expandable graphite into a diene rubber, and a manufacturing method of a tire using the same.
2. Description of the Related Art
Numerous studies have been conducted on the technique of blending hard substances, foaming agents, and hollow particulates into rubber to form microirregularities on the surface of the rubber so as to remove the water film formed on the surface of ice and improve the ice traction. However, there is the problem that these methods sometimes cannot result in the desired effects since the additives are brittle by nature and therefore part of the additives is made extremely fine or destroyed after mixing. Further, when mixing powders of these foreign substances to the rubber composition, generally the abrasion resistance of the rubber vulcanizate is remarkably decreased.
For example, examples of the blending of the above hard substances are disclosed in JP-A-60-258235 (i.e., ceramic fine powder), JP-A-2-274740 (i.e., cracked or divided plants), JP-A-2-281052 (i.e., metals). However, according to these methods, there are problems that the hardness of rubber is increased and the flexibilities of the rubber are spoiled, whereby the follow-up property of the tire to road becomes poor. In addition, examples of the above-mentioned hollow particulates are disclosed in JP-A-2-170840, JP-A-2-208336 and JP-A-4-5543. However, according to these methods, the hardness of the rubber is similarly increased or the hollow particles are broken during mixing. On the other hand, JP-A-11-35736 discloses the blending of thermoexpandable microcapsule as a hollow particle capable of improving the ice traction of rubber without increasing the rubber hardness and without being broken by a shearing force during mixing. However, the decrease in the abrasion resistance of the rubber vulcanizate with increase in the compounding amount is inevitable.